The inkjet recording system is a system in which an inkjet ink having high fluidity is ejected from fine head nozzles as ink particles to record an image on a printing paper placed opposed to the above nozzles, thereby making high speed printing possible with low noise, and therefore has become popular rapidly in recent years. As an ink used in such an inkjet recording system, various so-called nonaqueous pigment inks in which pigments are dispersed in nonaqueous solvents are proposed.
Compared with aqueous pigment inks, the nonaqueous pigment inks as described above are excellent in water resistance as well as in ejection stability, particularly continuous ejection properties and in decreasing image stains due to mist, however, are still problematic in that the pigment easily permeates into the inside of paper, thereby decreasing printing density. Therefore, in order to increase printing density, for example, a nonaqueous pigment ink in which nonaqueous resinous dispersion particles capable of dispersing pigments in a nonaqueous solvent are blended (Patent Document 1), and a nonaqueous pigment ink in which a water-soluble resin containing two or more amino groups in one molecule is added (Patent Document 2) are proposed.